1. Field of the Invention
The present invention relates to an image forming apparatus. More specifically, the present invention relates to an image forming apparatus that has a printing head for printing.
2. Background Information
Image forming apparatuses that have a thermal head or another such printing head have been known in the art. For example, Japanese Patent Application Publication No. 7-323587 discloses such image forming apparatus.
Japanese Patent Application Publication No. 7-323587 discloses a heat storing type printing apparatus (image forming apparatus) that has a thermal head (printing head), an intermediate transfer medium against which the thermal head is pressed with an ink sheet therebetween, a transfer device for transferring the ink that has been transferred onto the intermediate transfer medium onto a paper, and a thermal head moving mechanism for exerting pressure on the thermal head by the spring force of a tension coil spring. In this heat storing type printing apparatus, the ink from the ink sheet is transferred onto the intermediate transfer medium by the thermal head being pressed by the thermal head separation mechanism, and the ink transferred onto the intermediate transfer medium is transferred onto paper by the heat and pressure generated by the transfer device.
Heat transfer printers are also known as conventional image forming apparatuses. FIGS. 14 and 15 are perspective views showing the entire configuration of a conventional heat transfer printer. FIGS. 16 and 17 are perspective views of a pressing member and a support rod for describing the way in which the pressing member and the support rod are coupled to one another. FIG. 18 is a cross-sectional view for describing the pressing operation of a thermal head on a platen roller in the conventional heat transfer printer shown in FIGS. 14 and 15. The structure of the conventional heat transfer printer will now be described with reference to FIGS. 14 through 18.
As shown in FIGS. 14 and 15, a conventional heat transfer printer has a metal chassis 101, a thermal head 102 for printing, a platen roller 103, a metal support rod 104, a pressing member 105 having a toothed section, a pressing member 106 with no toothed section, a drive gear 107 having a resinous small gear 107a and large gear 107b for rotating the pressing member 105, a torsion coil spring 108, a resinous bearing plate 109 on which a platen roller bearing 109a is integrally formed, a resinous bearing plate 110 on which a platen roller bearing 110a is integrally formed, a motor 111, a motor bracket 112, and an intermediate gear 113.
Also, as shown in FIGS. 14 and 15, an insertion part 101c for mounting an ink sheet cartridge (not shown) is provided to the second side surface 101b that is opposite the first side surface 101a, on which the motor bracket 112 of the chassis 101 is mounted. Insertion holes 101d in which both ends of the support rod 104 are rotatably inserted are formed on the first side surface 101a and the second side surface 101b of the chassis 101. Also, the thermal head 102 is mounted in between the first side surface 101a and second side surface 101b of the chassis 101 so as to be capable of pivoting around a support axle 102a. The torsion coil spring 108 is mounted on the support axle 102a of the thermal head 102. This torsion coil spring 108 functions to urge the thermal head 102 in a direction away from the platen roller 103. Also, a head unit 102b, which is the bottom portion of the thermal head 102, is disposed so as to face the platen roller 103. Bent parts 102c that are pressed on by the pressing members 105 and 106 are formed above both ends of the head unit 102b of the thermal head 102.
As shown in FIGS. 16 and 17, insertion parts 104a near both ends of the support rod 104 have a shape of a circle with its sides cut off, and are snugly inserted respectively into similarly-shaped insertion holes 105a and 106a formed in the pressing members 105 and 106 such that the pressing members 105 and 106 do not rotate relative to the insertion holes 105a and 106a. Also, bearing supports 104b are formed on the ends of the insertion parts 104a of the support rod 104. The bearing supports 104b are rotatably supported in the insertion holes 110d of the chassis 101. Press springs 105b and 106b for exerting pressure on the bent parts 102c of the thermal head 102 are mounted on the pressing members 105 and 106, respectively. Also, as shown in FIG. 18, the toothed section of the pressing member 105 is disposed so as to engage the small gear 107a of the drive gear 107. The small gear 107a is disposed so as to rotate integrally with the large gear 107b. Also, the drive gear 107 is mounted on the first side surface 101a of the chassis 101 and is made to transmit the drive force from the intermediate gear 113 to the pressing member 105. The drive force of the motor 111 (see FIG. 15) mounted on the motor bracket 112 is transmitted to the large gear 107b of the drive gear 107 via the intermediate gear 113 (see FIG. 18).
In the operation of the conventional heat transfer printer described above and shown in FIG. 18, in which the thermal head 102 applies pressure to the platen roller 103, the drive force from the motor 111 (see FIG. 15) is transmitted to the toothed section of the pressing member 105 via the intermediate gear 113 and the large gear 107b and small gear 107a of the drive gear 107, such that the pressing member 105 pivots while being supported in the insertion holes 101d of the chassis 101. The bent part 102c on the side of the first side surface 101a of the chassis 101 is thereby pressed on by the press spring 105b of the pressing member 105. Also, since the pressing members 105 and 106 are mounted on the support rod 104 snugly so as not to rotate relative to each other, the support rod 104 and the pressing member 106 are pivoted by the pivoting of the pressing member 105. The bent part 102c on the side of the second side surface 101b of the chassis 101 is thereby pressed on by the press spring 106b of the pressing member 106, as shown in FIG. 15. As a result, the head unit 102b of the thermal head 102 is pressed on toward platen roller 103 against the urging force of the torsion coil spring 108.
In the conventional heat transfer printer shown in FIGS. 14 through 18, the insertion parts 104a at both ends of the metal support rod 104 are formed into an elongated circular shape in order to non-rotatably couple the pressing members 105 and 106, which exert pressure on the thermal head 102 and the support rod 104. Time-consuming cutting processes are required in order to form the metal support rod 104 into the elongated circular shape in this manner. Therefore, an unacceptably long time is required to form the members for exerting pressure on the thermal head 102. Furthermore, the diameter of the bearing supports 104b on the outer ends of the insertion parts 104a must be equal to or smaller than the width of the elongated circular portions of the insertion parts 104a. Accordingly, the same cutting processes are required to form the bearing supports 104b. Therefore, it takes even longer time to manufacture the components.
In the structure disclosed in Japanese Patent Application Publication No. 7-323587, although it is not clearly described, the thermal head separation mechanism appears to be pressed against the thermal head by the spring force of a single tension coil spring. Therefore, it is difficult to apply pressure to the thermal head with a sufficient amount of pressure during printing.
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved image forming apparatus that overcomes the problems of the conventional art. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.